Catharanthus roseus (your 'annual vinca') really hates overly moist soils! If that site is too wet for begonias, then it would sure be a problem for the Catharanthus.

Too much rainfall or improper irrigation could be a factor, perhaps?

Thanks Rhizo. I guess it could be over watering--though last summer was quite wet here in Atlanta too.....I'd rather have it be over watering than some disease or fungus that's hard to get rid of. Maybe I can try a real water-lover flower next!

Thanks again!

intense sunlight on the cement could be frying them ...

black stone or mulch can increase that ...

whats the stain on the cement..

and is that a patio table.. guests could be trampling them ...

and finally.. weedfree lawn .. overspray of weed killers or lawn fert ..

many alternative theories ...

ken

ps: what i dont get.. is why you have the plants jammed in what looks like a 6 inch border.. with rocks opposite the cement ... may as well try growing them in a parking lot.. re: reflected sun heat ... accumulating all day long.. and holding such late into the night ...

Thank you for your suggestions, Ken.

Sunlight could be an issue, but makes me wonder why flowers have thrived there in the past...puzzling.

The stain on the cement is simply dirt where water stands, as it does not drain fast--I could and should jet that off with the hose.

Nope, not a patio table, our guests sit under the lanai about 20 feet away. There is a fire pit near, but again not a trampling issue.

Overspray of weed killer is possible and I will check with my guy.....

Lastly, here is a photo that shows the area in more detail taken earlier this summer before the begonias died. Yes, they are situated in a 6 inch wide area between concrete and stones, but it looks fabulous next to the pool. :-)